1. Field of the Invention
The present invention relates to an improvement of a color imaging array and a color imaging device for use, e.g., in a color video camera.
2. Description of Background Art
The color video camera picks up an image of a subject and produces a video signal comprising three different color signals, for example, green, red and blue color signals. To this end, the image picked up by the video camera must be analyzed in three different colors. One approach to this is to employ a beam-splitting optical arrangement, for splitting the beam into three separate beams with three image sensors provided in the paths of the beams for sensing the respective colors.
The above arrangement, however, accompanies high manufacturing cost for three sensors and a beam-splitting optical, arrangement. Furthermore, it results in a bulky size of the unit.
Then, there has been proposed a single-sensor system which uses one CCD image sensor with an attached color mosaic filter to color encode the image. When compared with a black-and-white imaging system, such a single-sensor system for sensing the color image has less resolution.
To improve the color resolution, many approaches have been made. For example, U.S. Pat. No. 3,971,065 to Bayer teaches a color imaging array shown in FIG. 1a in which green filters are located at every other element positions along horizontal and vertical directions, and red and blue filters are located in alternate horizontal lines between elements with green filter. When this color imaging array is used in combination with a signal processing device designed for effecting a so-called interlaced readout, that is a readout effected in the order of odd horizontal lines from the ones with younger line number and then the even horizontal lines from the ones with younger line number, the odd rows in FIG. 1a, consisting of only red and green samples, are read out in sequence and displayed on the odd video field, followed by a display of green and blue elements alone from the even rows on the succeeding even field. This results in a yellow-cyan hue-flicker. Although this hue-flicker can be eliminated by employing a delay or memory means which delays each of red and blue signals by the time interval of one field for compensating the lacking color signal, for example, compensating the blue signal in the odd video field, the employment of one field memory results in high manufacturing cost. The Bayer's color imaging array is also discussed in IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. SC-13, NO. 1, FEBRUARY 1978 under title "Color Imaging System Using a Single CCD Area Array".
Another color imaging array such as shown in FIG. 1b is disclosed in Japanese Laid Open patent application (Tokkaisho) No. 55-55686 published Apr. 23, 1980. As apparent from FIG. 1b, the green filters are disposed in a manner of checkerboard, red filters are disposed in adjacent vertical lines in pairs which occur every other pair of vertical lines, and green filters are disposed in the remaining element positions. According to this arrangement, the red filters, when considered in the horizontal direction, are spaced 4 picture-element positions, and therefore, the resolution of red in the horizontal direction is poor. The same can be said to blue filters. This results in narrow Nyquist domain in horizontal direction.
A further color imaging array is shown in FIG. 2 in which the green, red and blue filters are in pairs in vertical direction, and such pairs of green, red and blue filters are disposed in a similar alignment as that shown in FIG. 1a. In other words, the first two rows in FIG. 2 correspond to the first row in FIG. 1a, and the next two rows in FIG. 2 correspond to the second row in FIG. 1a. When this arrangement of FIG. 2 is coupled with a signal processing device producing interlaced readout, the video signal of green, red and blue will be included in each of odd and even fields, and therefore, this arrangement will not result in any hue-flicker. However, the arrangement of FIG. 2 has such a disadvantage that each picture element occupies twice the area of that necessary in the imaging array of FIG. 1a or 1b. Therefore, when compared with the color imaging array of FIG. 1a or 1b, the color imaging array of FIG. 2 has a poor resolution.